TUESDAY, Oct. 15 (HealthDay News) -- People with moderate to severe psoriasis are at increased risk for chronic kidney disease and need to be closely monitored for kidney problems, a large new study suggests.

Researchers in Philadelphia analyzed data from nearly 144,000 people, aged 19 to 90, with psoriasis, and a comparison (control) group of nearly 690,000 adults without the condition.

During seven years of follow-up, people with psoriasis were more likely to develop chronic kidney disease than those in the control group. Those with severe psoriasis had a nearly two-fold higher risk of developing kidney disease and a more than fourfold higher risk of developing kidney failure requiring dialysis, according to a journal news release

Further investigation that focused on the amount of skin area affected by psoriasis showed that people with moderate to severe psoriasis were at greater risk of developing chronic kidney disease. People with moderate psoriasis have 3 percent to 10 percent of skin area affected, while those with severe psoriasis have more than 10 percent of skin area affected.

Psoriasis is a chronic condition involving scaly skin patches that can lead to itching, cracking and bleeding. As many as 7.5 million Americans have the autoimmune condition, according to the National Psoriasis Foundation.

Moderate and severe psoriasis affect more than 20 percent of patients worldwide, according to the study, which appears Oct. 15 in the journal BMJ.

Although the study found an association between having psoriasis and a higher risk of kidney problems, it did not establish a cause-and-effect relationship.

The researchers also found that the risk of chronic kidney disease linked to psoriasis increases with age. In patients aged 40 to 50 with severe disease, psoriasis accounted for one extra case of chronic kidney disease per 134 patients yearly. In those aged 50 to 60, it accounted for one extra case yearly per 62 patients.

Further research is needed to confirm the study findings, determine how psoriasis can cause kidney disease and examine how psoriasis treatment affects the risk for kidney disease, the researchers concluded.